Glycine-zipper-derived synthetic amino acid-containing peptides as amyloid-β aggregation inhibitors: structural and mechanistic investigations.

The hydrophobic C-terminus domain of amyloid-beta (Aβ) plays a vital role in the formation of neurotoxic assemblies that form senile plaques. Modified segment-based peptides are considered a promising strategy, as they can alter and inhibit the oligomerization and disorient the neurotoxic oligomers of Aβ. A glycine-zipped segment-based hexapeptide, Ile-Gly-Leu-Met-Val-Gly-OH (Aβ32-37), was selected for structural modifications, including replacement of key residues with unnatural amino acids. The synthesized hexapeptides inhibited Aβ42-induced cytotoxicity at 2-10 μM doses and rescued PC-12 cells. The most active peptide, Ile-Gly-Leu-Met-Val-Phg-OH (35), showed 96.4%, 90.1%, and 80.4% cell viability against Aβ42-induced toxicity at 10 μM, 4 μM, and 2 μM, respectively. Th-T and ANS fluorescence assays provide insight into the kinetics of inhibition. CD spectroscopy investigations revealed that peptide 35 restricted the formation of β-sheet conformation and the disintegration of pre-existing β-sheets. The disappearance of Aβ42 fibrillary networks in electron microscopy (HRTEM and STEM) confirmed the absence of Aβ42 aggregation. DLS study endorsed these findings by adding an in-depth mechanistic understanding of the inhibition process. In silico studies reveal binding interactions between Aβ42 and the peptide 35, corroborating the experimental observations (Kd = 8.75 nM). We conclude that peptide 35 reduces Aβ aggregation, exhibits β-sheet-breaking propensity, and lacks cytotoxicity, highlighting its promise as a potential therapeutic for AD.